1. Field of the Invention
The present invention relates to a pressure-variable valve device and, more specifically, to a pressure-variable valve device suitable for use as a shunt valve embedded in the human body to adjust the pressure of the spinal fluid or the like, and to a set-pressure adjusting device therefor.
2. Description of the Prior Art
Japanese Patent Application Laid-Open No. 60-40063 discloses a technique for treatment for hydrocephalus or the like in which the pressure of the spinal fluid or the like is adjusted by providing in the flow passage of the spinal fluid or the like a shunt valve (branch valve) device in which the forward ends of arm portions on both sides of a fork-like plate spring are locked, and the forward end of a central arm portion is held in contact with a ball serving as a valve, and in which the base end portion of the fork is engaged with a spiral cam surface formed on a rotating member rotatable around a central axis, and the engagement base portion of the spring is moved in the axial direction of the rotating member in accordance with the rotation of the cam surface as a result of the rotation of the rotating member to vary the deflection amount of the spring, thereby varying the pressure applied to the ball by the spring. In this shunt valve device, a ratchet having claws on the peripheral surface is formed integrally with the rotating member, and two engagement members are arranged opposite to the claws of the ratchet, each engagement member being rotatable around a fulcrum situated in the intermediate portion with respect to the longitudinal direction and having at both ends engagement pawls which can be engaged with the claws of the ratchet. Further, magnets are mounted to the engagement members such that the adjacent end portions of the two engagement members are of the same polarity. When a magnetic field is applied in one direction from outside, the two engagement members rotate in the same direction around their respective rotation axes to cause the ratchet to rotate in a direction corresponding to the direction of the above rotation. Next, a reverse magnetic field is applied to restore the two engagement members to the original rotating positions. By repeating these operations, the rotating position of the rotating member is adjusted (FIGS. 10a through 10d and FIG. 11 of the above-mentioned publication).
However, in this set-pressure-variable shunt valve or pressure-variable valve device, there is the danger that an undesired change in the set pressure occurs in an environment in which the direction of the external magnetic field applied to the entire shunt valve varies. That is, when a patient suffering from hydrocephalus or the like, under whose scalp the shunt valve is embedded, undergoes inspection and diagnosis of the head by an MRI (magnetic resonance imaging) apparatus, the patient, in a typical case, moves the head portion to be inspected and diagnosed in various directions in the MRI apparatus with respect to the strong and spatially uniform main magnetic field applied in the Z-direction of the apparatus, with the result that there is applied to the shunt valve portion a magnetic field whose direction varies in the same sequence as when the rotating position of the rotating member of the shunt valve is adjusted, thereby causing an undesired deviation in the set pressure.
The present invention has been made in view of the above problem in the prior art. It is accordingly an object of the present invention to provide a pressure-variable valve device in which there is little danger of the set pressure being deviated even in the main magnetic field of an MRI apparatus, and a set-pressure adjusting device for such a valve device.
To achieve the above object, there is provided, in accordance with the present invention, a pressure-variable valve device which is adapted to be embedded in the human body and which is capable of changing a difference in pressure between an inlet-side duct and an outlet-side duct, the valve device comprising a rotating member capable of rotating around a central axis inside a valve-device main body to vary a set pressure of a valve, and a rotation control mechanism for controlling the rotation of the rotating member, wherein the rotation control mechanism includes at least one permanent magnet structure supported by the valve-device main body so as to be capable of making a linear reciprocal translation in the valve-device main body, and a displacement transmission mechanism for rotating the rotating member in a direction corresponding to the direction of the translation of the permanent magnet structure.
In the pressure-variable valve device of the present invention, there are provided xe2x80x9cat least one permanent magnet structure supported by the valve-device main body so as to be capable of making a linear reciprocal translation in the valve-device main body, and a displacement transmission mechanism for rotating the rotating member in a direction corresponding to the direction of the translation of the permanent magnet structurexe2x80x9d, so that, by applying to a portion in the vicinity of the permanent magnet structure a magnetic field which causes the permanent magnet structure to make a translation movement in a direction corresponding to the direction of rotation of the rotating member by the displacement transmission mechanism (When there are a plurality of permanent magnet structures, the direction of translation of each permanent magnet structure is made the same as the direction of the torque applied to the rotating member), it is possible to rotate the rotating member in a desired direction. Further, in the pressure-variable valve device of the present invention, the rotating member is xe2x80x9ccapable of rotating around a central axis inside a valve-device main body to vary a set pressure of a valvexe2x80x9d, so that, by rotating the rotating member, it is possible to change the set pressure of the valve device, that is, the difference in pressure between the inlet-side duct and the outlet-side duct.
Further, in the pressure-variable valve device of the present invention, the permanent magnet structure is xe2x80x9csupported by the valve-device main body so as to be capable of making a linear reciprocal translation in the valve-device main bodyxe2x80x9d, so that, when the pair of magnetic poles (N, S) of the permanent magnet structure are simultaneously exposed to a magnetic field of the same direction and of actually the same strength like the main magnetic field in the Z-direction of an MRI apparatus, the forces causing the permanent magnet structure to make a translation are balanced, the forces applied to the magnetic poles being of the same magnitude and opposite directions. Thus, the permanent magnet structure is not actually caused to make a translation movement, and no torque is imparted to the rotating member, so that there is no danger of the rotating member being caused to rotate. That is, even when a person in whose body a pressure-variable valve device of the present invention is embedded is placed in the strong main magnetic field of an MRI apparatus for inspection or diagnosis, there is little danger of the rotating member of the valve device making an unexpected rotation and little danger of the set pressure of the valve device being changed.
In the valve device of the present invention, as long as it is possible to change the difference in pressure between the inlet-side duct and the outlet-side duct, the valve of the valve device may be of the type which normally keeps the flow passage closed and allows the inlet-side duct to communicate with the outlet-side duct when the set pressure is reached (normally-closed type), or of the type which normally keeps the valve flow passage open and in which the size of the aperture of the valve flow passage determines the difference in pressure between the inlet-side duct and the outlet-side duct (normally-open type). In the case of the former type, the set pressure is changed or adjusted by changing or adjusting the pressure at which the closure of the valve flow passage by the valve is canceled, and in the case of the latter type, the flow rate varies by changing or adjusting the aperture size of the valve flow passage throttled by the valve, thereby changing or adjusting the set pressure. Here, the terms: xe2x80x9cinlet-side ductxe2x80x9d and xe2x80x9coutlet-side ductxe2x80x9d mean ducts, conduits or flow passages at the inlet and outlet of the valve device.
There is no particular restriction regarding the way the rotating member is supported as long as it is capable of rotating around the central axis. The term xe2x80x9ccentral axisxe2x80x9d means the central axis of rotation or the rotation axis. The configuration of the rotating member is typically substantially symmetrical with respect to the central axis. Strictly speaking, however, it may also be asymmetrical. Further, the central axis, that is, the rotation axis may be offset from the central portion of the rotating member. At the time of rotation, the rotation member may move or not move along the rotation axis.
The permanent magnet structure typically consists of a permanent magnet having magnetic poles of opposite polarities at both ends. However, it is only necessary for the structure to behave as one permanent magnet as a whole with respect to an external magnetic field, and there is no particular restriction regarding the construction for magnetizing the interior of each structure. For example, the entire structure may consist of a permanent magnet, or one or more permanent magnets may be fixed or embedded at one or a plurality of positions. Further, in some cases, the magnetic pole may be situated at a side surface in the vicinity of an end portion so that the influence of the magnetic field formed by the set-pressure adjusting device arranged on the body surface may be easily had.
Preferably, the rotation control mechanism has a pair of magnet structures, and the displacement transmission mechanism is constructed such that, when substantially the same external magnetic field is applied to the pair of magnet structures, mutually balancing, reversely directed torques are imparted to the rotating member.
In this case, due to the influence, for example, of an inclined magnetic field, etc. applied in the MRI apparatus in order to provide a resonance frequency which differs from place to place, the magnitudes of the magnetic fields applied to the N-pole and the S-pole of the permanent magnet structure are different, so that, even when a force in the translating direction which is of some magnitude as a whole is applied to the permanent magnet structures, the pair of magnet structures impart mutually balancing torques to the rotating member. Thus, there is little danger of the rotating member being caused to rotate unexpectedly.
Preferably, the rotation control mechanism includes a pair of permanent magnet structures which are substantially opposed to each other in a diametral direction with respect to the central axis of the rotating member and which are capable of making a translation movement substantially in parallel in a direction crossing the diametral direction, the structures respectively having magnetic poles of the same polarity at an end on the same side with respect to the direction in which translation movement is possible, and a displacement transmission mechanism which causes an adjacent portion of the rotating member to move in a direction (the same direction) corresponding to the direction of the translation movement of one of the pair of permanent magnet structures, and which causes the adjacent portion of the rotating member to move in a direction (the same direction) corresponding to the direction of the translation movement of the other permanent magnet structure.
In this case, there are provided xe2x80x9ca pair of permanent magnet structures which are substantially opposed to each other in a diametral direction with respect to the central axis of the rotating member and which are capable of making a translation movement substantially in parallel in a direction crossing the diametral direction, the structures respectively having magnetic poles of the same polarity at an end on the same side with respect to the direction in which translation movement is possiblexe2x80x9d. Thus, when exposed to a magnetic field which is uneven or which is not uniform like the inclined magnetic field of an MRI apparatus, the pair of permanent magnet structures having magnetic poles of the same polarity at an end portion on the same side receive a force which causes them to make a translation movement in the same direction as long as the magnetic field is an abnormal magnetic field having a singular point. Further, there is provided xe2x80x9ca displacement transmission mechanism which causes an adjacent portion of the rotating member to move in a direction (the same direction) corresponding to the direction of the translation movement of one of the pair of permanent magnet structures, and which causes the adjacent portion of the rotating member to move in a direction (the same direction) corresponding to the direction of the translation movement of the other permanent magnet structurexe2x80x9d. Thus, when one of the pair of permanent magnet structures is caused to make a translation movement in one direction, an adjacent portion of the rotating member moves in the above direction to receive a force causing rotation in one direction, and the other permanent magnet structure which is substantially diametrally opposed thereto with respect to the central axis of the rotating member is also caused to make a translation movement in the same direction, that is, the above-mentioned direction, to cause the adjacent portion of the rotating member to move in the above direction and generate a force which causes the rotating member to rotate in the other direction. As a result, the rotation of the rotating member is mutually restrained or inhibited. Thus, even when inspection or diagnosis is conducted by an MRI apparatus or the like, it is possible to minimize the danger of the rotating member being caused to rotate unexpectedly. As a result, there is little danger of the set pressure of the valve device being unexpectedly changed by the rotation of the rotating member.
On the other hand, by forming a magnetic field which causes one of the pair of magnet structures to move in one direction and causes the other magnet structure to move in the other direction in the vicinity of at least one magnetic pole of each permanent magnet structure, an additive torque which causes portions of the rotating member diametrally opposed to each other to move in opposite directions is imparted to the rotating member, with the result that the rotating member receives torques in the same direction from the pair of permanent magnet structures, and is rotated in that direction, thereby making it possible to change the set pressure of the valve device in correspondence with the rotation.
For the pair of permanent magnet structures to impart mutually balancing opposite torques to the rotating member in a magnetic field inclined in one direction, it is possible to adopt, instead of the construction in which there are provided xe2x80x9ca pair of permanent magnet structures which are substantially opposed to each other in a diametral direction with respect to the central axis of the rotating member and which are capable of making a translation movement substantially in parallel in a direction crossing the diametral direction, the structures respectively having magnetic poles of the same polarity at an end on the same side with respect to the direction in which translation movement is possiblexe2x80x9d, a construction in which xe2x80x9cthe structures respectively have magnetic poles of opposite polarities at an end portion on the same side in the direction in which a translation movement is possiblexe2x80x9d, and, regarding the displacement transmission mechanism, it is possible to adopt in stead of the construction xe2x80x9cwhich causes an adjacent portion of the rotating member to move in a direction (the same direction) corresponding to the direction of the translation movement of one of the pair of permanent magnet structures, and which causes the adjacent portion of the rotating member to move in a direction (the same direction) corresponding to the direction of the translation movement of the other permanent magnet structurexe2x80x9d, it is possible to adopt a construction which causes an adjacent portion of the rotating member in one or the other direction upon the translation movement of one of the pair of permanent magnet structures in one or the other direction, and which xe2x80x9ccauses the adjacent portion of the rotating member in one or the other direction upon the translation movement of the other permanent magnet structure in one or the other directionxe2x80x9d. In the latter case, between the other magnet structure and the rotating member, there is further provided a displacement transmission mechanism, by means of which the displacement direction is reversed.
In these cases, the end portion at which the permanent magnet structure has a magnetic pole is typically an end edge of the structure. However, in some cases, it may also be some other portion such as a side surface in the vicinity of the end portion.
The displacement transmission mechanism may be constructed so as to convert the continuous transmission movement of the permanent magnet structure to a continuous rotation of the rotating member as it is. Typically, however, there is provided a one-direction clutch mechanism which makes an intermittent rotation by a unit pitch upon one translation movement of the permanent magnet structure in one direction.
In the valve device of the present invention, the displacement transmission mechanism preferably has a ratchet which coaxial with the rotating member and is formed integrally with the rotating member, and an engagement pawl connected to each permanent magnet structure so as to engage with an adjacent portion of a claw of the ratchet when each permanent magnet structure makes a translation movement. When making a translation movement in one direction or in the direction opposite thereto, the permanent magnet structure imparts a torque to the ratchet, so that there are provided a pair of engagement pawls for each permanent magnet structure.
In this case, each of the pair of engagement pawls connected to the permanent magnet structure may be in the form of a one-way clutch which imparts a torque to a claw of the ratchet in a translation movement in the corresponding direction and which imparts practically no torque to a claw of the ratchet in a translation movement in the returning direction. However, the rotation control mechanism preferably has a restraining spring or jumper spring provided with a restraining engagement end portion one end of which is engaged with the valve-device main body to cooperate with the engagement pawl of the permanent magnet structure to cause the rotating member to intermittently rotate in one-pitch unit of the claws of the ratchet and the other end of which is elastically pressed against the claw of the ratchet, wherein the restraining spring is constructed so as to restrain the rotation of the rotating member due to the pair of permanent magnet structures at the end of the restraining engagement end portion with a weak restraining force permitting the rotation of the rotating member. One end of the restraining spring may be fastened to the valve-device main body or simply locked thereto.
In this case, the restraining spring is constantly held in press contact with a claw of the ratchet at least to a slight degree, so that, even if the portion (e.g., the head) in which the valve-device is embedded is abruptly moved or if a slight mechanical impact is applied to the embedded portion, the ratchet is locked so as to prevent it from rotating freely to minimize the danger of unexpected rotation of the ratchet, thereby making it possible to minimize the danger of unexpected change in the set pressure of the valve device.
As long as it is integral with the rotating member, the ratchet may be integrally formed of resin or the like, or its components may be separately formed of metal or the like, fastening them together so as not to make relative rotation.
The permanent magnet structure typically has an elongated hole to be engaged with a guide pin formed in the valve-device main body so as to allow sliding in one direction. In this case, the displacement direction and the movable range of the permanent magnet structure can be reliably restricted due to the engagement between the guide pin and the elongated hole. However, as long as the permanent magnet structure can be supported so as to be capable of making a linear reciprocal translation movement in one direction without involving any play, and, typically, as long as it can be supported so as to be capable of making a linear reciprocal sliding movement, it is possible to adopt some other means to restrict the direction and range of the one-way displacement of the permanent magnet structure.
It is desirable that the components of the pressure-variable valve device be formed, as far as possible, of a material which is practically free from the fear of being seen in the image or disturbing the image when performing imaging by an MRI (magnetic resonance imaging) apparatus, that is a so-called MRI-free material. For example, it is desirable that a magnetic material be not used in the components other than the permanent magnet structure, which should constitute a permanent magnet. Further, when, for example, the MRI apparatus is of the type which utilizes proton NMR, it is desirable to use a material which is completely or relatively free from a resonance condition that is very close to the nuclear magnetic resonance condition of the hydrogen atoms to be observed in the portion to be inspected, such as the human head. Thus, it is desirable that the components of the pressure-variable valve device other than the permanent magnet structure (e.g., the valve-device main body and the rotating member) be formed of an MRI-free plastic material (e.g., silicon resin, polycarbonate or the like) or an MRI-free non-magnetic metal material. Since it is something to be embedded in the body, it goes without saying that an material harmful to the human body should be avoided.
To apply a predetermined magnetic field to a portion in the vicinity of one or a pair of permanent magnet structures in order to cause at least one of the permanent magnet structures of the pressure-variable valve device to make a translation movement to rotate the rotating member, a magnetic field generating means is arranged in close vicinity to each permanent magnet structure. Thus, the set-pressure adjusting device consists of such a magnetic field generating means. The magnetic field generating means typically consists of an electromagnet in which a soft magnetic substance of high magnetic permeability is inserted into a solenoid coil. The number of electromagnets may be one or two according to the number of magnet structures, or four or more according to the number of magnetic poles of the magnetic structures.
The valve device has a set-pressure signal generating means so that the set-pressure condition of the valve device can be detected from outside. The signal may be a magnetic signal like a static magnetic field (e.g., the strength or direction of a magnetic field or the way time-dependent fluctuations are effected), an electric signal like a static electric field (e.g., the strength or direction of an electric field or the way time-dependent fluctuations are effected), an electromagnetic signal like an electromagnetic field, or other kinds of signal. Since the rotating position of the rotating member varies according to the set pressure, it is possible to directly detect the rotating position or adopt an arrangement in which some other factor (e.g., the axial position) varies according to the rotation, detecting this other factor.
The valve device is designed to be embedded in the human body for a medical purpose or the like. Typically, it is designed to be surgically embedded in the human body in order to be used as a shunt valve for ventricle/abdominal-cavity shunt, ventricle/ventriculus-cordis shunt, etc. so that the pressure of the relevant fluid in the body can be non-invasively adjusted to treat hydrocephalus, brain tumor, arachnoid cyst or the like, and it can have a size of approximately several cm or less which is suitable for use when adjusting the pressure of spinal fluid or the like.